Electrolytic reduction cell

ABSTRACT

A COMPOSITE ELECTRICAL CONDUCTOR ADAPTED TO CONTACT AN ELECTRODE IN CURRENT TRANSMITTING ENGAGEMENT. A FERROUS METAL PLATE IS AFFIXED TO THE FREE END OF A FERROUS METAL ROD ADAPTED TO BE EMBEDDED IN THE ELECTRODE. A SOFT ALUMINOUS PLATE IS ROLL BONDED ALONG ONE FACE TO THE FERROUS PLATE AFFIXED TO THE ROD. AN ALUMINUM CONDUCTOR ROD IS WELDED TO THE ALUMINOUS PLATE ROLL BONDED TO THE FERROUS PLATE AND IS ADAPTED TO BE CONNECTED TO A SOURCE OF ELECTRIC CURRENT.

May 18, 1971 w. D. FINNEGAN ELECTROLYTIC REDUCTION CELL 2 Sheets-Sheet 1Filed sept. 2s. 196e ML me /7/1//VEGA N INVENTOR.

Evi/2? Mlm-HMH United States Patent Ofce 3,579,432 ELECTROLYTICREDUCTION CELL Walter D. Finnegan, Spokane, Wash., assignor to KaiserAuminum & Chemical Corporation, Oakland, Calif. Filed Sept. 23, 1968,Ser. No. 761,421 Int. Cl. B01k 3/04; C23b 5/70 U.S. Cl. 204-279 7 ClaimsABSTRACT F THE DISCLOSURE plate and is adapted to be connected to asource of electric current.

BACKGROUND OF THE INVENTION This invention relates to electricalconductors useful in electrolytc cells employing electrodes supported byindividual bars or rods of conductor material It is particularlyapplicable to electrolytc cells for the reduction of aluminum containingcompounds, e.g. alumina, for the production of aluminum.

The metal aluminum is extracted from aluminum-bearing compounds such asalumina (A1203) by electrolysis from a molten salt bath or electrolyte.In the production of aluminum by the conventional electrolytc process,commonly referred to as the Hall-Heroult process, the electrolytc cellcomprises in general a steel shell having disposed therein a carbonlining. The bottom of the carbon lining together with a layer ofelectrolytically produced molten aluminum which collects thereon duringoperation serves as the cathode. One or more consumable carbonelectrodes is disposed from the top of the cell and is immersed at itslower extremity into a layer of molten electrolyte which is disposed inthe cell. In operation, the electrolyte or bath, which is a mixture ofalumina and cryolite, is charged to the cell and an electric current ispassed through the cell from the anode to the cathode via the layer ofmolten electrolyte. The alumina is dissociated by the current so thataluminum is deposited on the liquid aluminum cathode and oxygen isliberated at the carbon anode, forming carbon monoxide and carbondioxide gas. A crust of solidified electrolyte and alumina forms on thesurface of the bath, and this is usually covered over with additionalalumina.

In the conventional electrolytc process, use has been made of two typesof electrolytc cells, namely that commonly referred to as a prebrakecell and that cornmonly referred to as a Soderberg cell. With eithercell, the reduction process involves precisely the same chemicalreactions. The principal difference is one of structure. In the prebakedcell, the carbon anodes are prebaked before being installed in the cellwhile in the Soderberg, or self-baking anode cell, the anode is baked insitu, that is, it is baked during operation of the electrolytc cell,thereby utilizing part of the heat generated by the reduction process.The instant invention is applicable to either cell.

As has been discussed above, a carbon anode is used in aluminumreduction cells. The electrical current required to eifect reduction isconveyed from a bus bar through an anode rod assembly to the stub offerrous metal embedded in and supporting the anode. Normally, the anoderod consists of a rectangular copper bar or rod that is joined to theferrous stub. In some instances the copper rod or bar is joined to aferrous metal hanger to which ferrous metal stubs are attached. Ineither case, a connnection is required between the anode rod and a fer-3,579,432 Patented May 18, 1971 rous metal member. Herein, the ferrousmetal assembly shall be referred to in all cases as a stub whether theconnection be directly to the stub or via a hanger which is subsequentlyconnected to the stub. Service requirements dictate that the union 'bestrong, have low electrical resistance and be unaffected by the heatthat it is necessarily exposed to during use.

A similar arrangement is used in the cathode. One or more ferrous metalrods or collector bars are embedded in the carbonaceous portion of thecathode. The ferrous metal rod or collector bar is connected to aflexible connector which in turn is connected to the negative or cathodebus bar of the cell.

Copper is particularly suited to use as the anode rod or bar. However,copper is becoming in increasingly short supply and the price of theavailable material has risen sharply, Accordingly, a substitute materialmust be found. Aluminum metal or aluminum alloys such as that known aselectrical conductor grade (EC) aluminum are good electrical conductorsand would seem suited for this purpose. However, the oxide film normallypresent on aluminum effects current conductivity from the aluminum tothe ferrous metal. Moreover, in prior attempts to use aluminum anoderods it has been found that a bolted connection is not satisfactory foraluminum because joint resistance becomes excessive as relaxation occursthrough creeps of the aluminum member. Solders are melted due to theheat of the cell. Fusion welding and brazing are ruled out because abrittle intermetallic layer is formed between the aluminum ller metalsand the ferrous metal member of the assembly. The instant invention wasdeveloped against this background in the art.

SUMMARY OF THE INVENTION It is an advantage of the instant inventionthat it provides a reliable electrical union between the two dissimilarmetals, aluminum and ferrous metal. This is accomplished by providing asolid phase bonded aluminumferrous transition insert made by rollbonding to connect the alumium conductor rod (which term is to beunderstood as including a flexible connector) to the ferrous metalmember of the electrode assembly.

In one application of the instant invention, an electrolytc reductioncell is provided which comprises a lining which denes a cavity adaptedto contain an electrolyte, and an anode disposed within the cavity. Aflexible bus conductor is connected to an anode bus bar above the cavityin combination with an electrical connection plate attached to theflexible bus conductor and positioned above the cavity. A ferrous metalstub is embedded in and supports the anode. A ferrous metal plate havinga soft aluminous plate roll bonded along one face thereto is affixed tothe end of the stub not embedded in the anode. An aluminum conductor rodis welded to the aluminous plate roll bonded to the steel plate. Meansare provided for holding the conductor rod and electrical connectionplate in current transmitting contact.

Normally, at least the bottom section of the cell lining is part of thecathode. A ferrous metal rod or collector bar is embedded in this partof the lining. A ferrous metal plate may be affixed to the end of therod not embedded in the electrode. If the instant invention is appliedto this assembly, a soft aluminous plate is roll bonded along one faceto the ferrous plate aixed to the rod. An aluminum conductor rod (orflexible connector) is Welded to the aluminous plate roll bonded to theferrous plate and is adapted to be connected to the cathode bust bar.When an electrical power source is connected across the anode bus barand cathode bus bar, electrical current will flow between the anode andcathode via the electrolyte contained in the cavity.

According to one embodiment of the invention the ferrous metal plate iswelded to the ferrous metal stub. In

another embodiment, the ferrous metal plate is bolted to the stub, thehead of the bolt may be recessed in a hole provided in the aluminousplate of the assembly. Another variation of the bolted joint involvesroll bonding a second ferrous metal plate to the opposite side of thealuminous plate from the rst ferrous plate. In this way when thealuminous plate is welded to the aluminum conductor rod the ferrousplates are adapted to extend along opposite sides of the stub and thebolt can pass through both of them.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevational viewpartly in section of a reduction cell embodying the principles of theinstant invention.

FIG. 2 is a front elevational view partly in section of an electrolyticcell embodying the principles of the instant invention.

FIG. 3 is a partial view of a connection between the rod and stub inaccordance with the principles of the instant invention.

FIG. 4 is a partial view showing another form of the connection betweenthe rod and stub in accordance with the instant invention.

FIG. 5 is a View of another connection between the rod and stub inaccordance with the principles of the instant invention.

FIG. 6 is a View of another connection between the rod and stub inaccordance with the principles of the instant invention.

DETAILED DESCRIPTION Referring now to the drawings in which the samereference numerals have been applied to corresponding parts, and withparticular reference to FIG. l, an aluminum reduction cell 10 is shownhaving a carbon lining 12 which defines a cavity indicated generally at14 adapted to contain a molten aluminum pad 16 and an electrolyte orbath 18 consisting essentially of alumina dissolved in cryolite. Carbonlining 12 is supported by a shell 20 of suitable material such as steel,a layer of insulation 22 being provided between lining 12 and shell 20.Within the shell 20 is disposed one or more carbon anodes 24. Anodes 24may be of the prebaked type as shown in FIG. 1 or the continuous orself-baking or Soderberg type as shown in FIG. 2. A ferrous metal stub26 is embedded in and supports the anode. As shown in FIG. 1, stub 26may in reality consist of two pieces, a bracket plate 26a and a stub 26proper. An anode bus bar 28 is positioned above cavity 14.

A ferrous metal plate 30 is affixed in an appropriate manner to the endof stub 26 not embedded in the anode. If desired, additional materialsuch as a furane binder or cast iron may be used to insure that the stub26 is properly embedded in and supports the anode 24. As has beendiscussed hereinabove and as shall be discussed more fully hereinafter,the ferrous metal plate may be affixed in diverse -ways to the end ofstub 26. In the embodiments shown in FIGS. 1 and 2, ferrous metal plate30 is fusion welded to stub 26. A soft aluminous plate 32 is roll bondedalong one face to plate 30. Commercially pure aluminum, i.e. that knownas 1100 grade aluminum is acceptable for this purpose or electricalconductor grade (EC) aluminum is also acceptable for this purpose. Inany event, the aluminum or aluminum base alloy should be readilyplastically deformable at the bonding temperature.

Although there is still some conjecture as to exactly what happens in aroll bonding operation, it is thought that elongation of the bondelement fragments oxide films on both the aluminous element and theferrous element of the sandwich and allows metal-to-metal contactwithout an interfering oxide film.

An aluminum anode or conductor rod 34 is welded to the aluminous plate32 roll bonded to plate 30. Appropriate means such as clamp 36 areprovided for holding the conductor rod 34 and anode bus bar 28 incurrent transmitting contact. A ferrous metal cathode rod or collectorbar 38 is connected to a cathode bus bar 40 in an appropriate manner asby exible connector 42. The cathode rod 38, shown here embedded incarbon lining 12, is in any event positioned in the cell 10 so that whenan electrical power source, not shown, is connected across the anode busbar 28 and the cathode bus bar 40, electrical current will flow betweenthe anode 24 and the cathode system, comprising the collector bar 38,lining 12 and molten aluminum pad 16 via the electrolyte or bath 18contained in cavity 14.

As shown in FIGS. l and 2 the connection between cathode rods 38 andflexible connectors 42 can be made in a manner similar to the connectionbetween the anode rod 34 and stub 26. That is, a transition insert ofthe same type can be used with the ferrous metal plate 30 of the insertaffixed to the end of the collector bar or cathode rod 38. The softaluminous plate 32 is roll bonded along one face to the ferrous plate 30affixed to the stub or collector or cathode rod 38. The exibleconnector, or aluminum conductor rod, is welded to the aluminous plate32 roll bonded to the ferrous metal plate 30. It is then connected in anappropriate manner to cathode bus bar 40 which in turn is connected to asource of electric current as has been explained previously.

The embodiment shown in FIG. 3 is similar to that of FIG. 1 with theexception that only a single rather than a double stub 26 is connectedby means of the transition insert. The anode rod 34 is welded -to thealuminous plate 32 and the ferrous metal stub 2'6 is welded to theferrous metal layer or plate 30.

FIGS. 4 and 5 show a slightly different assembly. Here, the transitioninsert contains a layer of ferrous metal 30 and a layer of aluminousmaterial 32 or, in the case of FIG. 5, a central ferrous metal layer 30to which layers of aluminous material 32 have been roll bonded on bothsides. The construction shown in FIGS. 4 and 5 permit the use of abolted union because the bolting is effected between the plate 30 of theinsert and the ferrous metal stub 26 of the assembly, a union that isserviceable in reduction cells. The aluminous layers or plates 32 of theinsert can be trimmed back to leave a projecting length of ferrous metalplate 30. 11n such case, the projecting length of ferrous metal must beof sufficient cross sectional area .to carry the electrical current.Alternatively, as shown in FIG. 5, a hole large enough to accommodatethe head of the attaching bolt can be cut in the aluminous plate 32 anda smaller one in the ferrous metal plate 30 to accommodate the shaft ofthe bolt. The aluminous plate 32 would carry current to the portions ofthe ferrous plate 30 that are held in contact with the stub 26 bybolting pressure. In such case, the current carrying capacity of theferrous plate 30 depends on the cross sectional area. of bolting contactand a relatively thin layer of ferrous metal would suflice.

In FIG. 6 is shown au assembly composed of an insert containing acentral aluminous plate 32 to which ferrous metal plates 30 have beenroll bonded on both sides. This construction also enables bolting to beused to connect the anode assembly to a stub 26 or similar member.

As an example of the practice of the instant invention, plates of 3Athick electrical conductor grade aluminum were degreased and abrasivelycleaned using a grit belt sander. Electrical conductor grade aluminum is99.45% pure aluminum. This is essentially a slightly higher purity thancommercially pure or 1100 grade aluminum which is 99% pure aluminum.Plates of 1A" to 1/2" thick type 304 stainless steel Were also degreasedand belt sanded using a 150 grit abrasive belt. The composition of 304stainless steel may be expressed as 0.06% carbon, 1.84% manganese, 0.02%phosphorous, 0.01% sulfur, 0.54% silicon, 9% nickel, 18% chromium, 0.25%molybdenum, 0.21% copper, and 0.10% cobalt with the remainderessentially iron. The composition limits of type 6 304 stainless steelare lil-20% chromium, 8-1l% nickel, Metallographic examination of thesamples of 1100 0.08% maximum carbon, manganese 2.0% maximum, 1008explosion bounded and the 1100/ 1020 after an the balance essentiallyiron. The Cleaned plates were laid exposure of one month at 800 F.revealed an appreciable together so the sanded faces were in ContactWith each intermetallic layer in the explosion bounded and no other. Thelaid up pack was heated to 550 F. and reduced intermetallic formation inthe roll bonded material. The

by rolling in a single pass through a rolling mill to a thickroll bondedsample passed a bend test while the explosion ness of 0.79 inch.Material was cut into 3% inch wide bonded material failed. Examinationof a failed explosion and 5 inch long7 pieces. An aluminum anode rod wasgas bonded piece showed that fracture accurred along an metal-arc fusionwelded to the aluminum layer and the intermetallic layer.

stainless steel layer of the transition insert piece was fusion lo Whilethere have been shown and described hereinabove welded to the ferrousmetal member of the anode assempossible embodiments of this invention,it is to be underbly (the stub). Nine anode assemblies made using thisstood that the invention is not limited thereto and that roll bondedmaterial were installed in a 30,000 ampere various changes, alterations,and modilications can be prebaked electrode aluminum reduction cell.Eight simimade thereto Without departing from the spirit and scope larassemblies were made with an explosion bonded or thereof as defined inthe appended claims wherein:

Welded 1100 grade aluminum-1008 carbon steel. The cai'- What is claimedis;

bon steel known commercially as 1008 carbon steel has 1. A compositeelectrical conductor adapted to coria carbon content that must notexceed 0.15 Weight pertact iii current transmitting engagement anelectrode which cent. The nominal composition of 1008 carbon steel iscomprises:

0.10 maximum carbon, 0.25-050 manganese, 0.040 max- (a) a ferrous metalrod or stub adapted to be embedded imum phosphorous, 0.050 maximumsulfur, balance essenin the electrode;

tially iron. Five of the explosion welded assemblies failed (b) aferrous metal plate afl'ixed to the end of the rod by delamination inuse but all the assemblies made in not embedded in the electrode;

accordance with the instant invention operated satiSfaC- (c) a softaluminous plate roll bonded along one face torily. The superiority ofthe instant invention is tentato the ferrous plate affixed to the rod;

tively attributed to a superior metallurgical union achieved (d) analuminum conductor rod welded to the alumiby the roll bondingtechniques. nous plate roll bonded to the ferrous plate and adapted ASeries Of artificial aging tests Were the Conducled to be connected to asource of electric current.

to compare the efficacy 0f VariOUS alloys and bondmg 2. The appartus ofclaim 1 wherein the ferrous plate is techniques. These testssubstantiated that the roll bonding Welded to the stub.

technique provides a superior material for the instant in- 3. The a anusof claim 1 wherein the ferrous late vention. The original materialthicknesses and alloys, rollis bolted tophe Stub. p

ing temperatures, and deformations are listed in Table I. 4 Theapparatus of claim 3 wherein the head of the All transition materialsused similar roll bonding procea dures. Plate materials were degreasedand then abrasive bolt 1S recessed m a hole PTOVlded 111 the alumlIlOuSplate.

round The packs were assembled and heated to or 5. The apparatus ofclaim 3 wherein a second ferrous c, slightly above rolling temperatureand then rolled in a plate is roll bonded to the opposite side of thealuminous Single pass through the rolling min. Table 11 summarizes platefrom the rst ferrous plate so that when the alumibend tests on aumaterials. nous plate is welded to the aluminum conductor rod the TABLEL RoLL-BONDED ALUMlNUn-STEEL FOR AGING TESTS Aluminum Steel NominalOriginal Qrigirial Nominal laying Rolling Reduction, Finish pack i Alloythick., in. Alloy thick., in. area temp.,u F. percent thick., in.

0 75 0.50 6 x 16" 700-740 16 1 05 Bllafirm"""ff 0 75 ggf 156,-,- so-ggg(i) (Sii D o 7g 0.25 3" x 12" 570 19 o si 1 Bilayer=one aluminum plateand one steel plate Der pack- Double blaVef=tW0 Steel plates in center,with two outside aluminum plates. 2 Bridge steel=a 0.26% carbon steelwith 0.33% Si and a maximum of 1.30% Mn. t

s 3003=0.6 Si; 0.7 Fe; 0.20 Cu; 1.0-1.5 Mn; 0.10 Zn; others 0.05 ea.,0.15 total, balance aluminum.

4 1020=0.180.23 C; 0.30-0.60 Mn; 0.040 P, max.; 0.050 S, max.; balanceiron.

TABLE H BEND TEST AFTER ELEVATED TEA/1 ferrous plates are adapted toextend along opposite sides PERATURE AGING of the stub and the bolt canpass through both of them. (Samples winch thick Slices) 6. The conductorof claim 1 wherein the ferrous metal t t re o F plate is a substantiallystainless steel alloy plate. Transition Time at w 7. The compositeelectrical conductor of claim 1 the material temperature 930 800 660 540ferrous metal rod of which is embedded in an electrode formed ofcarbonaceous material lmonth "d0"" OK""' 0K" References Cited EC Bfda ti1 0K 60 U @es e@ Broi'roiifffii UNITED STATES PATENTS oK OK do2,880,157 3/1959 'Wleugel 204-286X imonth 1o OK OK---- 65 3,424,6681/1969 Fischer 204286X 1100/100s 2 hr Broke.-. 8%-- OK FOREIGN PATENTS33; B 1,183,699 12/1964 Germany 20.1 243 O0/102 :2 maire-131515121 I 70JOHN H- MACK, Primary Examiner lmonth OK D. R. VALENTINE, AssistantExaminer l Roll bonded. 2 Explosion bonded. NoTis.-Broke=Fracture atinterface, no deformation, usually with U.S. C1. X.R.

finger pressure; OK=90 bend at interface, no separation; =Not tested;All five material combinations passed 00 bend, before elevated tempei'a-204-286 ture exposure.

